1. Field of the Invention
The present invention relates to a liquid crystal panel, and more particularly, to a parallax barrier liquid crystal panel for a stereoscopic display device and a fabrication method thereof.
2. Description of Related Art
To present, two-dimensional (2-D) devices have predominantly been used to convey information. Recently, three-dimensional (3-D) display devices have emerged from research and development as broadband communication networks allow high-speed delivery of large amounts of information.
In general, 3-D display devices display stereoscopic images using stereo vision principles. Parallax of vision perceived by both eyes is the primary key in displaying 3-D images. When the right eye and the left eye each see a 2-D image, the 2-D image perceived by each respective eye is transferred to the brain. The brain combines the two 2-D images into a 3-D image having depth, making the image look “real.”
Based upon the above principle, various display devices have been used to display 3-D images using 2-D images. For instance, stereoscopic display devices with specially designed glasses, stereoscopic display devices without the need for glasses, holographic display devices, and the like, have been developed. The disadvantages of stereoscopic display devices with specially designed glasses are numerous. Need for the specially designed glasses to see the 3-D image makes use of such devices inconvenient. The glasses themselves are generally uncomfortable to wear and feel unnatural.
Holographic display devices also pose disadvantages. Holographic display devices use laser beams to generate the 3-D image. Holographic display devices are generally large and expensive requiring large amounts of space. In contrast, stereoscopic display devices without special glasses use generally simple equipment and do not require separate accessories (i.e., specialized glasses). These stereoscopic display devices without glasses are generally divided into three categories: a parallax barrier type, a lenticular type and an integral photography type. Of these types, the parallax barrier type has been mainly used.
FIG. 1 shows a cross-sectional view illustrating a parallax barrier type stereoscopic display device according to the related art. As shown in FIG. 1, the parallax barrier type stereoscopic display device includes a liquid crystal display panel 10, a backlight 20 below the liquid crystal display panel 10, and a parallax barrier 30 between the liquid crystal display panel 10 and an observer 40. A left eye pixel L and a right eye pixel R are alternately formed in the liquid crystal display panel 10. A slit 32 and a barrier 34 are alternately formed in the parallax barrier 30. Each of the slits 32 and the barriers 34 form a stripe pattern. When light is emitted from the backlight 20, first light L1 passing through the left eye pixel L goes to the observer's left eye through the slit 32, while second light R1 passing through the right eye pixel R goes to the observer's right eye through the slit 32. Images displayed through the left and right eye pixels L and R have parallax information that humans can sufficiently perceive. Thus, the observer 40 sees 3-D images. However, since the slits 32 and barriers 34 are fixed, parallax barrier type display devices are used only for displaying 3-D images. Accordingly, stereoscopic display devices that switch between a 2-D mode and a 3-D mode have been developed.
FIGS. 2A and 2B are cross-sectional views illustrating a 2-D mode and a 3-D mode, respectively, of a stereoscopic display device having a parallax barrier liquid crystal panel according to the related art. As shown in FIGS. 2A and 2B, the stereoscopic display device includes a backlight 50, a main liquid crystal panel 60, and a parallax barrier liquid crystal panel 70 between the backlight 50 and the main liquid crystal panel 60. The main liquid crystal panel 60 includes first and second substrates 64 and 66, and a first liquid crystal layer 62 between the first and second substrates 64 and 66. Though not shown in the drawings, a plurality of pixel electrodes and thin film transistors (TFTs) are disposed in a matrix form on the first substrate 64, and a plurality of color filter patterns, a black matrix and a first common electrode are disposed on the second substrate 66.
The parallax barrier liquid crystal panel 70 includes third and fourth substrates 74 and 78, and a second liquid crystal layer 72 between the third and fourth substrates 74 and 78. A barrier electrode 76 having a stripe pattern is disposed on the third substrate 74, and a second common electrode 80 is disposed on the fourth substrate 78. The barrier electrode 76 and the common electrode 80 are transparent. First, second, and third polarizing plates 82, 84, and 86 are formed on the second substrate 66, between the main liquid crystal panel 60 and the parallax barrier liquid crystal panel 70, and below the third substrate 74, respectively.
In a 2-D mode, the parallax barrier liquid crystal 70 is in a white state when the parallax barrier liquid crystal panel 70 is driven in a normally white (NW) mode. When in a 2-D mode, as shown in FIG. 2A, no driving voltage is applied to the barrier electrode 76. Thus, the entirety of parallax barrier liquid crystal panel 70 is in a normally white state. Accordingly, all of the light emitted from the back light 50 is transmitted through the parallax barrier liquid crystal panel 70. As a result, an observer can see plane images (i.e., 2-D images) of the main liquid crystal panel 60.
In a 3-D mode, as shown in FIG. 2B, on the other hand, a driving voltage is applied to the barrier electrode 76, thus activating the second liquid crystal layer 72 between the barrier electrode 76 and the second common electrode 80. Accordingly, various zones of the parallax barrier liquid crystal panel 70 corresponding to the barrier electrode 76 shield light emitted from the backlight 50. Each of these light-shielded zones is referred to as a barrier-zone BZ having a black state. The zones between the barrier-zones BZ transmit light emitted from the backlight 50. Each of these light-transmitting zones is referred to as a transmission zone TZ having a white state. The barrier-zones BZ and the transmission-zones TZ act as a barrier and a slit, respectively, as the parallax barrier 30 shown in FIG. 1. Accordingly, a user can selectively convert the stereoscopic display device between a 2-D mode and a 3-D mode based on the On/Off states of the barrier electrode 76 by selecting a dimension mode. As a result, an observer can view 2-D images (i.e., plane images) and 3-D images (i.e., stereo images) from the same main liquid crystal display panel 60.
FIG. 3 is a cross-sectional view illustrating another stereoscopic display device having a parallax barrier liquid crystal panel according to the related art. Detailed explanations of parts already shown in FIGS. 2A and 2B will be omitted. FIG. 3 shows a stereoscopic display device including a main liquid crystal panel 60, a backlight 50, and a parallax barrier liquid crystal panel 70 similar to the stereoscopic display device of FIGS. 2A and 2B. However, the parallax barrier liquid crystal panel 70 of FIG. 3 is structurally different than the parallax barrier liquid crystal panel 70 of FIGS. 2A and 2B. In particular, partition walls 90 composed of transparent photo acryl, for example, are formed in transmission-zones TZ between the barrier-zones BZ of the liquid crystal layer 72. Accordingly, a boundary between the transmission-zones TZ and the barrier-zones BZ is distinctly defined when the stereoscopic display device selectively displays a 2-D image and a 3-D image.
As explained above, the related art stereoscopic display devices having the parallax barrier liquid crystal panel have certain advantages, such as the ability to selectively switch between a 2-D mode and a 3-D mode. However, the disadvantages of the related art stereoscopic display devices include low brightness and low sensory resolution in the 3-D mode. As the width of the transmission-zones TZ decrease, the sensory resolution increases. However, as a width of the transmission-zones TZ decrease, the aperture ratio also decreases, thereby reducing the brightness.
FIG. 4 is a conceptual plan view illustrating a screen in a 3-D mode of the related art stereoscopic display device having a parallax barrier liquid crystal panel. Characters R, G, and B represent red, green, and blue pixels of the main liquid crystal panel. As shown in FIG. 4, the width of a transmission-zone TZ is very small. Accordingly, the aperture ratio and the brightness of the display drastically decrease as the areas of the transmission-zones TZ are reduced. A corollary to this effect is that the sensory resolution decreases as the areas of the transmission-zones TZ are enlarged to increase the aperture ration and the brightness. As a result, the stereoscopic display device of the related art is structurally limited in displaying 3-D images due to reduced sensory resolution in maintaining some degree of brightness.